An optical axis adjusting mechanism is a mechanism for adjusting a direction of an optical axis of a camera. Generally, an adjusting part is provided inside an imaging unit housing, which leads to an inconvenient adjustment. For example, a Chinese Patent No. 201420778261.1 discloses a remote infrared camera adjusting device and an infrared camera with the same. In this patent, after an installation is completed, an adjusting device is located inside an imaging unit housing. Thus, during adjustment, the corresponding adjusting device is required to be adjusted before being installed into the imaging unit housing. If the direction of the optical axis is found to be inappropriate after the adjusting device is installed into the imaging unit housing with a camera body, the adjusting device and the camera body need to be taken out and adjusted again. Thus, it is inconvenient to installation and adjustment.